Metal‐chloride‐anion‐containing polymers with expanded π‐conjugation systems derived from through‐space interactions in the piperazinium ring

Reactions of N‐(2,4‐dinitrophenyl)pyridinium chloride (salt(Cl)) with H⁺MCl₄^?1 (M ≡ Fe and Bi) resulted in an anion exchange between Cl^? and MCl₄^? to yield Zincke salts with metal chloride anions, namely salt(Fe) and salt(Bi), respectively. Reactions of the Zincke salts with piperazine resulted in ring‐opening of the pyridinium ring, yielding ionic polymers with 5‐piperazinium‐2,4‐dienylideneammonium metal chloride units, namely polymer(Fe) and polymer(Bi). The corresponding model compounds were synthesized via reactions using salt(Bi) or salt(Cl) as starting materials. The UV–visible spectra of the polymers had absorption maxima at longer wavelengths than those of the model compounds. This indicated that the π‐conjugation system is expanded along the polymer main chain. Superconducting quantum interference device measurements indicated that polymer(Fe) was paramagnetic. Cyclic voltammetry analysis suggested that the polymers underwent electrochemical oxidation. © 2019 Society of Chemical Industry     

Peculiar sandwich-like π–π interaction regulating the nonplanarity of the model heme crystals

X-ray crystallographic analysis of bis(pyridine N-oxide) complexes of iron(III) porphyrinates has revealed that the two pyridine rings of the axial ligands correctly sandwich the porphyrin ring to induce the deformation of commonly observed S₄ saddled porphyrin ring.     

Review of electronic and optical properties of semiconducting π‐conjugated polymers: applications in optoelectronics

A general overview of the optoelectronic properties of π‐conjugated polymers is presented. Two types of polymer are discerned: interchangeable structures of the same energy (degenerate), such as polyacetylene; and non‐degenerate polymers, such as poly(para‐phenylene). The band structures of degenerate and non‐degenerate polymers are related to their conductivities in doped and non‐doped states. In both cases, disorder and impurities play an important role in conductivity. Polarons, bipolarons and excitons are detailed with respect to doping and charge transfers. Given the fibrillic nature of these materials, the variable range hopping (VRH) law for semiconducting polymers is modified to account for metallic behaviours. Optoelectronic properties—electroluminescence and photovoltaic activity—are explained in terms of HOMO and LUMO bands, polaron‐exciton and charge movement over one or more molecules. The properties of H‐ or J‐type aggregates and their effects on transitions are related to target applications. Device structures of polymer light‐emitting diodes are explicitly linked to optimising polaron recombinations and overall quantum efficiencies. The particularly promising use of π‐conjugated polymers in photovoltaic devices is discussed. Copyright © 2004 Society of Chemical Industry     

Organometallic synthesis of n‐type π‐conjugated polymers with dopant cation trapping sites and stability of n‐doping state against air

n‐Type π‐conjugated polymers comprising a 1,2,4‐triazole ring substituted by a benzo‐15‐crown 5‐ether (benzo15C5) subunit at the 4‐position of the 1,2,4‐triazole ring and n‐type aromatic rings such as pyridine‐2,5‐diyl and 2,1,3‐benzothiadiazole‐4,7‐diyl rings were synthesized by organometallic polycondensation. The UV‐visible spectra of the polymers exhibited absorption maxima (λ_max values) at a longer wavelength than that exhibited by 3,5‐bis(2‐bromopyridyl)‐4‐benzo15C5‐1,2,4‐triazole, revealing that their π‐conjugation system was expanded along the polymer chain. The polymers with the benzo15C5 subunit underwent an electrochemical reduction (n‐doping), and the corresponding oxidation (n‐dedoping) occurred at an unusually high potential in an acetonitrile solution of NaClO₄; the factor responsible for the unusually high oxidation potential was the stabilized n‐doping state that was attributed to the inclusion of Na⁺ in the 15C5 ring. The polymers with the benzo15C5 subunit exhibited a considerably higher stability of the n‐doping state in air than did those without this subunit. Copyright © 2012 Society of Chemical Industry     

Gold(I)‐Catalyzed Decarboxylation of Propargyl Carbonates: Reactivity Reversal of the Gold Catalyst from π‐Lewis Acidity to σ‐Lewis Acidity

A cationic gold(I)‐catalyzed decarboxylative etherification of propargyl carbonates to selectively produce propargyl ethers is reported. In the reaction the gold(I) catalyst shows a distinct σ‐Lewis acidity rather than the commonly observed π‐Lewis acidity, and thus catalyzes the decarboxylation of a variety of propargyl carbonates to give the corresponding propargyl ethers with high selectivity. This reaction represents a rare example of the tunable reactivity of cationic gold(I) complexes between σ‐Lewis acidity and π‐Lewis acidity.

     

Diastereoselective Synthesis of Six‐Membered Carbocyclic Spirooxindoles via 6π‐Electrocyclization of 3‐Dienylidene‐2‐ oxindoles

The Wittig reaction of isatin derivatives with Morita–Baylis–Hillman bromides of cinnamaldehydes afforded 3‐dienylidene‐2‐oxindoles. These trienes were converted into the corresponding spirooxindoles in a stereoselective manner in refluxing toluene in good yields. The diastereomeric spirooxindoles could be obtained stereoselectively by adding a catalytic amount of palladium(II) acetate via the palladium‐catalyzed isomerization of EEE‐trienes to ZEE‐trienes followed by a more facile 6π‐electrocyclization process. The obtained spirooxindoles could be further functionalized by palladium‐catalyzed oxidative arylation, thionation with Lawesson’s reagent, catalytic hydrogenation and Friedel–Crafts‐type reaction.

     

Flexible Metal‐Free Memory Electronic Made of π‐Conjugation‐Interrupted Hyperbranched Polymer Switch and Reduced Graphene Oxide Electrodes

A flexible metal‐free flash memory device with reduced graphene oxide films as electrodes and diarylfluorene‐based π‐conjugation‐interrupted hyperbranched polymers (CIHPs) as active switches is reported. Two CIHPs, named PCzPF and PCzPF‐PF, are synthesized via BF₃?Et₂O‐catalyzed fluorenol’s Friedel–Crafts reaction, where the PCzPF‐PF is designed by the decoration of hindrance functional groups, i.e., bulky 9‐phenyl‐fluorenyl (PF) moieties, at the end‐groups of PCzPF. Both of the two CIHPs exhibit excellent solubility and thermal stability. The PCzPF‐based device exhibits no switching effect while the PCzPF‐PF‐based device shows a flash type memory effect, indicating the incorporation of PF groups plays a critical role in realizing electrically bistable behaviors. In particular, the optimized memory exhibits a high ON/OFF ratio of > 3.0 × 10³, long retention time of up to 1.2 × 10⁴ s, and high mechanical stability. This work opens a new avenue for metal‐free memory electronics through a low‐cost and full‐solution process approach.     

High activity of rare earth tetrahydroborates for ring‐opening polymerization of ω‐pentadecalactone

Ring‐opening polymerization of ω‐pentadecalactone (PDL) by tetrahydroborate complexes of rare earth metals, Ln(BH₄)₃(THF)₃ (Ln = La ( 1 ), Nd ( 2 ), Y ( 3 )), was studied. These complexes showed high activity for PDL polymerization in THF at 60°C. Among the complexes 1 – 3 , the neodymium complex 2 was most active. The obtained poly(PDL) was demonstrated to be hydroxy‐telechelic by ¹H‐NMR and MALDI‐TOF MS spectroscopy. Biodegradation of the poly(PDL) in compost at 60°C was investigated, where 18% weight loss of the samples was observed after 280 days. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Synthesis and characterization of α‐butyl‐ω‐N,N‐dihydroxyethylaminopropylpolydimethylsiloxane

α‐Butyl‐ω‐N,N‐dihydroxyethylaminopropylpolydimethylsiloxane, a monotelechelic polydimethylsiloxane with a diol‐end group, which is used to prepare polyurethane–polysiloxane graft polymer, was successfully synthesized. The preparation included five steps, which are hydroxyl protection, alkylation, anionic ring‐opening polymerization, hydrosilylation, and deprotection. The products were characterized by FTIR, GC, LC‐MS, ¹H NMR, and elemental analysis. The results showed that each step was successfully carried out and the targeted products were synthesized in all cases. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

An ionic liquid‐based polymer with π‐stacked structure as all‐solid‐state electrolyte for efficient dye‐sensitized solar cells

An ionic liquid based polymer, poly(1‐ethyl‐3‐(acryloyloxy)hexylimidazolium iodide) (PEAI), was synthesized and employed as electrolyte to fabricate all‐solid‐state dye‐sensitized solar cells. The photophysical properties of PEAI were studied by UV–vis absorption spectroscopy and photoluminescence spectroscopy. PEAI exhibited significant hypochromism and red shift in UV–vis absorption spectra and large Stokes shifts in photoluminescence spectra, indicating the formation of a novel π‐stacked structure in which the imidazolium rings in the side chain were stacked. Without iodine in its preparation, DSC with PEAI electrolyte achieved a conversion efficiency of 5.29% under AM 1.5 simulated solar light irradiation (100 mW cm^?2). The side‐chain imidazolium π‐π stacking in PEAI played a key role in the holes transport from the photoanode to the counter electrode. Both the open‐circuit voltage and short‐circuit current density showed decreases with the increase in the content of iodine in PEAI electrolyte. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Delocalized π‐electrons in 2‐oxazoline rings resulting in negatively charged nitrogen atoms: revealing the selectivity during the initiation of cationic ring‐opening polymerizations

The inventory of the single‐crystal X‐ray structures of aliphatic and aromatic 2‐oxazolines, namely 2‐nonyl‐2‐oxazoline, 2,2′‐tetramethylenebis(2‐oxazoline) and 2‐phenyl‐2‐oxazoline, reveals significant delocalization of π‐electrons along the N? C? O segment. The delocalization of π‐electrons is stabilized by inductive and resonance contributions of the side‐chains; in 2‐phenyl‐2‐oxazoline, also π‐arene interactions between the benzene ring and the C? N and the C? O bond stabilize the crystalline phase. This delocalization gives a partial negative charge to the nitrogen atom and a partial positive charge to the oxygen atom. The partial negative charge of the nitrogen atom makes this atom the exclusive reaction partner also for highly reactive non‐selective cations, which explains the regioselectivity of electrophilic attacks in cationic ring‐opening polymerizations. Copyright © 2011 Society of Chemical Industry     

π-Conjugated soluble palladium poly-ynes: Synthesis and fluorescence properties

Insertion of thiophene-2,5-diyl, or 1,4-phenylene into palladium poly-ynes by the polycondensation of dihalide complexes PdCl₂(PR₃)₂ (R = Ph o γ n-butyl) with a di-yne monomer (obtained from the reaction of equimolar quantities of p-diethynyl-benzene with 2,5-diiodothiophene or 1,4-diiodobenzene) affords a series of palladium poly-ynes 1–6. The polymers/oligomers, soluble in common organic solvents, exhibit strong fluorescence at the excitation of UV-visible light at room temperature. The emission intensity of the polymers/oligomers with thiophene-2,5-diyl is 3–17 times stronger than that of the analogous polymers without thiophene-2,5-diyl. Polymers with phenyl substituted phosphine ligands emit stronger emission than those only with n-butyl phosphine ligands. The effects of molecular weight, ligands, solvents, and concentration on the fluorescence properties are also investigated. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 1657–1665, 1997     

Synthesis of ω‐amino‐α‐phenylcarbonate alkanes and their polymerization to [n]‐polyurethanes

Aliphatic [n]‐polyurethanes have recently been synthesized from ω‐isocyanato‐α‐alkanols or, more traditionally, by cationic ring‐opening polymerization of cyclourethanes or by the Bu₂Sn(OMe)₂‐promoted polycondensation of ω‐hydroxy‐α‐O‐phenylurethane alkanes. For the latter procedures, the conditions employed do not seem to be suitable for highly functionalized monomers. In contrast, the polymerization of ω‐amino‐α‐phenylcarbonate alkanes is expected to occur under milder conditions. ω‐Amino‐α‐phenylcarbonate alkanes have been synthesized from 6‐aminohexanol (1) and 3‐aminopropanol (6). The procedure involves the N‐Boc protection of the amino group, followed by activation of the alcohol. Removal of the N‐Boc affords the corresponding ω‐amino‐1‐O‐phenyloxycarbonyloxyalkane hydrochlorides. Other oligomeric comonomers between 1 and 6 have been prepared. The polymerization of these precursors takes place in the absence of metal catalysts to afford the corresponding linear and regioregular [n]‐polyurethanes. The procedure described is useful for the preparation of stable ω‐amino‐α‐phenylcarbonate alkane derivatives, which possess varied chain lengths between the terminal functions. These monomers yield [n]‐polyurethanes having various structures starting from just two aminoalkanols. The polyurethanes were obtained in high yields, with reasonable molecular weight and polydispersity values, and they were characterized spectroscopically and thermally. These studies reveal constitutionally uniform structures that are free of carbonate or urea linkages. Copyright © 2010 Society of Chemical Industry     

Hydrogen‐bonding interaction between poly(ε‐caprolactone) and low‐molecular‐weight amino compounds

The specific interactions between several low‐molecular‐weight diamino compounds and poly(ε‐caprolactone) (PCL) have been investigated by FT‐IR. It was found that PCL and 3,3′‐diaminodiphenylmethane (3,3′‐DADPM) interact through strong intermolecular hydrogen bonds in the blend. Thermal and mechanical properties of PCL/3,3′‐DADPM blends were investigated by DSC and tensile measurements, respectively. The glass transition temperature of the blend increases while both the melting point and the elongation‐at‐break of the blend decrease with the increase of 3,3′‐DADPM content. Besides 3,3′‐DADPM, several other low‐molecular‐weight compounds containing two amino groups, such as o‐phenylenediamine or 1,6‐diaminohexane, were also added into PCL and the corresponding blend systems were investigated by FT‐IR and DSC. The effect of the chemical structure of the additives on the properties of PCL is discussed. © 2001 Society of Chemical Industry     

Polyaniline doped with α, ω‐alkanedisulfonic acids: preparation and characterization

The use of α, ω‐alkanedisulfonic acid, HO₃S(CH₂)_nSO₃H (n = 1, 4, 6 and 12), as a dopant for polyaniline (PANi) was investigated. This series of disulfonic acids with varying chain lengths were synthesized and used in the doping of PANi. The doped polymers showed conductivity in the range 10^?2 to 10^?1 S cm^?1. Thermal studies showed that the doped polymers, depending on the chain length of α,ω‐alkanedisulfonic acid, were stable up to ca 300 °C and the thermal stability decreased with increasing dopant chain length. The thermal stability of α,ω‐alkanedisulfonic acid‐doped PANi was higher than that of alkanesulfonic acid‐doped PANi which typically degrades around 250 °C, suggesting a moderately broader processing window for α,ω‐alkanedisulfonic acid‐doped PANi for blending with other thermoplastics. Copyright © 2012 Society of Chemical Industry     

Sodium Borohydride‐Nickel Chloride‐Methanol Catalytic System for Regioselective Reduction of Electron‐Rich Conjugated Dienes and Reductive Cleavage of Allyl Esters Involving π‐Allylnickel Intermediates

The regioslective reduction of electron‐rich dienes to monoolefins and the reductive cleavage of allyl esters were fulfilled by employing a sodium borohydride‐nickel chloride‐methanol catalytic system with exceedingly simple manipulations and high functional group tolerability. Both of the reductive reactions may involve π‐allylnickel intermediates generated from fresh nickel boride.     

Cyclopropanation of Strained Alkenes by Palladium‐Catalyzed Reaction of 3‐Trimethylsilyl‐ or 3‐Pinacolatoboryl‐1‐arylallyl Acetates

The palladium‐catalyzed cyclopropanation of strained alkenes with 3‐trimethylsilyl‐ or 3‐pinacolatoboryl‐1‐arylallyl acetate derivatives is described. This reaction gives cyclopropanation products in good to high yields with a single diastereomer, and the key step is likely to involve the formation of a palladacyclobutene complex from the α‐trimethylsilyl‐ or α‐pinacolatoboryl‐σ‐allylpalladium complex.     

Synthesis of nitropyridine‐based π‐conjugated polymers and their chemical properties

π‐Conjugated poly(3‐nitropyridine‐2,5‐diyl) ( PPy‐3‐NO₂ ), poly(3,3′‐dinitro‐2,2′‐bipyridine‐5,5′‐diyl) ( PBpy‐3,3′‐diNO₂ ), and a poly(arylene ethynylene) type polymer consisting of a 3,3′‐dinitro‐2,2′‐bipyridine unit ( PAE‐1 ) were synthesized by Cu‐promoted Ullmann coupling reaction and Pd‐catalyzed coupling reaction. PPy‐3‐NO₂ and PAE‐1 were soluble in organic solvents such as DMSO, DMF, and chloroform, and gel permeation chromatography analysis showed a number average molecular weight (M_n) of 9,300 and 12,300, respectively. PPy‐3‐NO₂ gave intrinsic viscosity, [η], of 0.53 dL g^?1 in DMF. PBpy‐3,3′‐diNO₂ had somewhat lower solubility. The polymers exhibited a UV–vis peak at about 430 nm. PPy‐NO₂ received electrochemical reduction at ?1.5 V versus Ag⁺/Ag in acetonitrile, and gave an electrochemical redox cycle in a range from 0 to ?1.1 V versus Ag⁺/Ag in an aqueous solution. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 1763–1767, 2006